The first magnetic wire recorder was created in 1899 by a Danish Engineer called Valdemar Poulsen (1869 – 1942). Commercial magnetic wire recorders for dictation and telephone recording were made almost continuously from the 1920s onwards, but the real heyday of wire recording was in the 1940s through to the mid-1950s.

No mention of where these things came from? The first I've seen wasn't a recorder, it was a radio detector: a loop of moving wire with two coils touching, antenna on the first coil and headphones on the second, and a magnet to restore the wire afterwards. "Marconi Magnetic Detector." Nonlinear effects presumably demodulated the RF. I guess it was a Coherer with a single giant iron filing.

Hmm. Was this the origin, or did wire recorders predate 1910 or so? Firesign Theater of course insists that they were invented by native americans who recorded civil-war era theater dramas...

In response to kendallcp: it works! I did it with tape back in the early '70s, and unknown to me at the time, Joe Dundovic of Nortronics (tape heads) was experimenting with it too. Tape goes "gracefully" into distortion when overdriven, and the only thing you have to watch out for with PWM is reaching the point when your duty cycle disappears and audio peaks slam the supply rails into the head. This can be obviated with some form of limiter ahead of the PWM circuit, or by comparing your audio waveform with a 'peaky' clock, rather than a triangle, to generate the PWM.

Another neat trick that works, sort-of, is to get rid of the AC bias altogether. It's possible to predistort the audio waveform in a manner opposite to the hysteresis-loop function of the recording process, although this requires fancy phase compensation as well as the nonlinear transfer. This gets rid of the "biased-tape noise," and really improves the high-frequency performance. The tradeoff is 'modulation noise,' which can be eliminated by applying a sort of 'dithering,' which puts the biased-tape noise right back. Such fun!